1. Field of the Invention
The present invention relates to a synchronization lag control apparatus and method for controlling a synchronization lag between a video signal and an audio signal when reproducing a multiplexed information signal formed from a coded video signal and a coded audio signal.
2. Description of the Prior Art
In various storage methods of particular contents such as package media and broadcasting, there may arise an error during reproduction by a reproduction apparatus.
For example, in a reproduction apparatus for reproducing a video signal from a digital video disc (DVD) containing audio/video signal compression-coded by way of the MPEG (Moving Picture Experts Group) 2 method of data compression technique (hereinafter, this compression technique will be referred to as MPEG2) or other discs containing video signals, there arise various errors including an incorrectable error of an error correction code due to fingerprints or scars on the disc, temporary disability of data read out due to an external shock, bugs in control circuits such as various decoders, an error caused by that a compressed data such as a multiplexed data, video data, and audio data is not matched with the format.
Conventionally, in the aforementioned disc reproduction apparatus, each of the aforementioned error factors was coped with respectively for evasion of the errors and adverse affects. For this, various circuits are required to cope with the respective errors, which has increased the entire circuit size.
Moreover, in a case when an error cannot be recovered completely by the corresponding means, even if the synchronization (AV synchronization) between an audio data and a video data is obtained at a reproduction start, there arises a lag in the AV synchronization as the time lapses.
The AV synchronization lag may be caused by use of an external synchronization signal, for example, when a video synchronization signal from an external device has a phase not matched with the clock used in the reproduction apparatus, or when changing the speed control in a so-called Karaoke, or when continuously decoding discontinuous audio frames called audio gap in the aforementioned DVD.
It is therefore an object of the present invention to provide a synchronization lag control apparatus and method capable of preventing errors with a reduced circuit size without preparing particular countermeasures for respective error factors.
There can be considered various error factors, which finally cause an AV synchronization lag. There are also error factors which directly cause the AV synchronization lag.
As for the errors which causes the aforementioned AV synchronization lag, no particular countermeasures are taken. Instead, by detecting an AV synchronization lag, the synchronization lag is corrected.
For correcting the AV synchronization lag, the AV synchronization is established by skip/repeat/halt and restart of a video signal with respect to an audio signal. It is also possible to carry out skip/repeat/halt and restart of an audio signal. However, for the human sense, the skip/repeat/halt and restart of an audio signal causes a strong feeling of disorder compared to that of a video signal. Consequently, as has been described above, the quality of reproduction is maintained as good as possible by carrying out skip/repeat/halt and restart of a video signal with respect to an audio signal.
In order to achieve the aforementioned object, the synchronization lag control apparatus according to the present invention employs control means for resetting a system time clock serving as a system reference time with a time management information in video decoding means, so that this reset time is compared to a time management information of video decoding means or audio decoding means, so as to control a synchronization lag between a video signal and an audio signal according to a result of the comparison.
Moreover, in order to achieve the aforementioned object, the synchronization control method according to the present invention employs control means for resetting a system time clock serving as a system reference time with a time management information used in decoding a video signal, so that this reset time is compared to a time management information of video decoding means or audio decoding means, so as to control a synchronization lag between the video signal and the audio signal according to a result of the comparison.
Moreover, in order to achieve the aforementioned object, the synchronization lag control apparatus according to the present invention employs control means for resetting a system time clock serving as a system reference time with a time management information in video decoding means, so that this reset time is compared to a time management information of the video decoding means or audio decoding means, so as to use a result of the comparison for matching a decoding timing of the video signal with a decoding timing of the audio signal.
Moreover, in order to achieve the aforementioned object, the synchronization control method according to the present invention employs control means for resetting a system time clock serving as a system reference time with a time management information used in decoding a video signal, so that this reset time is compared to a time management information of video decoding means or audio decoding means, so as to use a result of the comparison for matching a decoding timing of the video signal with a decoding timing of the audio signal.